In a Code Division Multiple Access (CDMA) based cellular network all users in the same cell or in different cells may share the same frequency spectrum simultaneously. In spread spectrum transmission, the interference tolerance enables universal frequency reuse. This enables new functions such as soft handover, but also causes strict requirements on power control. Due to the universal frequency reuse, the connection of a radio terminal, e.g. a mobile terminal, mobile station or user equipment to the cellular network can include several radio links. When the radio terminal is connected through more than one radio link, it is said to be in soft handover. If, in particular, the radio terminal has more than one radio link to two cells on the same side, it is in softer handover. Soft handover is a form of diversity, increasing the signal-to-noise ratio when the transmission power is constant.
At network level, soft handover smoothes the movement of a mobile terminal from one cell to another. It helps to minimize the transmission power needed in both uplink and downlink.
Thus, a radio terminal of a network subscriber can transmit the same information on a plurality of redundant transmission parts that are set up parallel via a radio transmission interface from the cellular network to the radio terminal or from the radio terminal to the cellular network in order to achieve an optimal transmission quality. Such a transmission structure is called macrodiversity. The redundant transmission paths can be dynamically set up and cleared down while the radio terminal changes its location. The information sent out by the radio terminal in the transmission frames on various transmission paths can be merged in the trans-mission network at combination points at which respectively two transmission paths are combined into a single transmission path in one transmission direction (uplink) and the single transmission path is divided into two transmission paths in the other transmission direction (downlink). A corresponding network architecture is described for example in the U.S. Pat. No. 6,198,737 B1.
In order to obtain the most efficient RAN architecture, which is based on using the advantageous characteristics of IP, some functionality is relocated between network elements. According to a recent new architecture, a network element, known as Base Station Controller (BSC) or Radio Network Controller (RNC) is no longer required, although this functionality must remain in the RAN architecture. Therefore, a location of a combining point, e.g. MDC point, can no longer be centralized for all base stations in the RAN. Consequently, some RNC functionality has been transferred to the base stations in order to enable soft handover and associated signaling to happen along the shortest path, producing minimum delay and signaling load to those paths of the network where this is not necessary. This new RAN architecture is described e.g. in the White Paper “IP-RAN, IP—the future of mobility”, Nokia Networks, 2000.
In such a new RAN architecture, the MDC point can be selected dynamically e.g. by a serving base station instead of having this functionality in one pre-selected point like the RNC in the conventional RAN architecture or in the base station that initiates the call. In the new RAN architecture, base stations are able to act as MDC points.
However, in order to select the MDC point dynamically, the corresponding network node or entity needs up-to-date information of the RAN network, e.g. its parameters such as link state, link utilization, node utilization, MDC load, and any other QoS-related parameters. When any change of a parameter happens, the change parameter needs to be distributed among the network nodes or entities. In addition, any change of a parameter will invoke a tide of messages or packets in the network for keeping all network nodes updated. If the known flooding scheme as described e.g. in J. Moy, “OSPF Version 2”, IETF specification RFC1583, 1994 is used, a parameter change can, in the worst case, invoke as many messages or packets as twice the total number of links in the RAN. Thus, updating traffic may become a source of network congestion itself. Furthermore, the flooding scheme is not scalable with an increase of the dimension of the RAN. Given the on-changing nature of the RAN, a scalable and efficient distribution scheme is therefore required for this purpose.